Combine harvesters have on-board grain tanks to hold the harvested crop before being discharged to a trailer through an unloading system. Grain tanks are typically designed to include a narrowed region or trough towards the bottom of the tank in which a transverse screw conveyor (or cross auger) of the unloading system is located. The tanks are normally designed to avoid horizontal surfaces on which grain could become trapped, and so the sidewalls are either vertical or sloped. During unloading, the grain is carried away by the cross auger and the sloping sidewalls steer the grain into the trough to allow for complete emptying of the tank.
The cross auger rotates on a substantially transverse rotation axis. A cover plate is commonly provided to partially cover the cross auger and regulate the flow of grain from the tank to the auger. The cover plate typically leaves an opening to both the front and to the rear thereof through which the grain passes. In some designs of grain tank grain only flows through one of the openings once the level has dropped during an unloading event. Reduced unloading rates have been observed in some instances when the grain level drops below one of the openings in this way.